Calomel SSL Validation add-on gives comprehensive information about the SSL cipher strength of the current connection just with a click.
It scores the connection on the following items: if the certificate was valid, if the fully qualified host name is equal to the common name the certificate was registered for and the strength of the cipher and cipher key length.
This add-on offers several other useful functions also. In the "Preferences" section, you can choose to hide titles and icons in each of the tabs, which is useful to stop people looking over your shoulder to see what sites you have open. Another option is you can disable annoyances like blinking text and gif animations commonly seen in ads.
You can install Calomel SSL Validation at Mozilla add-on repository.